The xiao mouthpiece is certainly interesting, Paddler, but clearly in the same general league as the Quena and Giorgi. My experience with any of these is that they do not share the efficiency of our transverse flutes. I put this down to the jet having to “battle” the returning airwave, rather than offering it something to grab and manipulate. But maybe I’m wrong? I’d be pleased to hear.
Or maybe these flutes just don’t suit my face?
You might reasonably ask hey, what about the low whistle? It’s played vertically, or at least, in line, not transversely.
I’d argue the same. I’ve not heard a low whistle that can produce anywhere as good a tone as a transverse flute. It would be fair to point out that the whistle doesn’t allow the player to modify the windway in the same way we flute players intuitively modify our windways (lips). But perhaps the test would be does it equal the flute in the middle of the range, say 2nd octave D?